Trump is set to appear at Atlantic Aviation on May 10 in South Bend, Ind., at 7 p.m. His campaign noted that this will be the president’s ninth rally in Indiana — and his second in South Bend — since announcing his presidential campaign in 2015.

Michael Glassner, chief operating officer of Donald J. Trump for President, Inc., said that Trump will travel to Indiana to promote the GOP's tax-cut bill and also focus on boosting voter turnout in the midterm elections to protect the party's slim majority in the Senate.

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“The President is excited to return to South Bend to tout the benefits that his historic tax cuts are providing Hoosier families throughout Indiana, and to remind them what an important role they’ll play in expanding our GOP majority in the Senate in the mid-term elections this fall,” Glassner said in a Thursday statement.

Donnelly is one of 10 Senate Democrats up for reelection in a state that Trump carried in 2016. Indiana has been a top target for Republicans since the president won it by 19 points.

Republicans are going into November facing strong electoral headwinds, but the Senate map is more favorable than the House since they have more opportunities to flip seats. The GOP is looking to expand its narrow one-seat majority in the upper chamber.

There were also be primaries for House races, but the one that has drawn the most attention is the open-seat race to replace Messer. Greg Pence, the brother of Vice President Pence, is the leading candidate for the GOP nomination in Indiana’s 6th District. It's a safe GOP seat, and the eventual nominee will be favored in the general election.